This first lab is aimed at taking you through the end-to-end process of writing and running a basic computer program. As with all things in life, we will learn in this lab that becoming a programmer requires you to learn a number of other things along the way.
In software development/engineering parlance, we typically describe a scenario as a workflow, which can be thought of as a series of steps that are possibly repeated. The workflow of programming can loosely be defined as follows:
As we will learn later in the course, development environments such as Visual Studio (from Microsoft) and MonoDevelop (an open source implementation similar to Visual Studio) basically shield you from the details of understanding the workflow in detail. We think it is important that you learn this workflow from day one, because many types of software development don’t always have the easiest software development tools. You will be able to use fancy tools later.
The following is the code for a very well-known program, Hello, World!:
1 2 3 4 5 6 7 8 9 10 11 12 | using System;
namespace Comp170
{
public class Hello
{
public static void Main ()
{
Console.WriteLine ("Hello World!");
}
}
}
|
This program is deliberately simple, so you can type it into a text editor (Emacs is recommended but your instructor may introduce you to a different editor, subject to availability in the lab) quickly and become familiar with how to create, edit, and save a program. Perform the following steps. (You are free to deviate but may want to consider following the steps religiously at least once to ensure you were successful.)
Open the text editor. This can usually be done from your GUI’s start menu.
Create a folder anywhere you like (e.g. in Documents) and name it hello. (This can be done through the desktop shell (e.g. Windows Explorer or Apple Finder.) As a general rule, we recommend that you start any new programming project in its own folder that is free of other folders/files. Clutter is a great enemy of those who aspire to become good programmers.
When you start in Emacs, you are in what is known as scratch mode. Typical of a sketchpad used by artists, this is where you can start typing right away. You can now begin typing in the text above. Keep in mind that the exact formatting is not important at this stage; however, as we progress in this course, you’ll want to pay attention to how your code is formatted. (With most text editors, it is possible to reformat your code to make it beautiful. More on that later.)
Once you have entered the text, you will want to save it, just as if you were saving a file in your word processor. (In the Emacs text editor, you use Control-x, Control-s. You will want to save the file with the name Hello.cs. If you are using a graphical text editor (like the case) then you will usually be able to save from the File menu, much like you would do in a regular word processor. Keep in mind, however, that you will eventually want to learn the keyboard shortcuts for your editor as much development work in the real world happens from the command line and remote terminal sessions (e.g. web and embedded systems development).
If all has gone well, you will now have a version of Hello, World in a file named Hello.cs in a folder named hello (located in Documents).
Now we are going to learn how to compile this program. For this, you will need to open a shell. On Linux and OS X, the shell is opened by launching Terminal. On Windows, open a Mono Command Prompt, as discussed above (or use one you left open). Again to find it:
Now you need to learn how to “move around” using the shell. The command shell basically awaits user input and does whatever it is told (and does nothing otherwise). You’ll begin by using the “cd” command to change your working directory to where you saved Hello.cs. Note: Replace Dr. Thiruvathukal’s login id gkt by your login id. Also note for Mac/Unix examples that his machine is called macaroni.
If you did everything right, you can do this on Windows:
C:\Windows\System32> cd C:\users\gkt
C:\Users\gkt> cd Documents\hello
C:\Users\gkt\Documents\hello>
Mac/Linux:
$ cd Documents/hello
If you are on OS X or Linux, you can list the directory using the ls command. If the output you see here does not match, make sure you are in the hello folder:
$ ls
macaroni:hello gkt$ ls
Hello.cs
$ pwd
/Users/gkt/Documents/hello
If you’re on Windows, can list the contents of the directory using dir:
C:\Users\gkt\Documents\hello>dir
Volume in drive C has no label.
Volume Serial Number is 2C13-C918
Directory of C:\Users\anh\Documents\hello
01/16/2012 06:07 PM <DIR> .
01/16/2012 06:07 PM <DIR> ..
11/04/2011 08:20 PM 646 Hello.cs
...
If you are unable to see Hello.cs at this stage, you need to go back and check all previous steps. It is entirely possible you did not create the folder or save properly. If you think you completed these steps, this is a good time to ask the instructor or teaching assistant for help.
Assuming you are able to see Hello.cs in the hello folder, we are now ready for the good stuff*~~the technical term we use when we are about to learn something that we need to know how to do *for life. We’re going to compile the Hello.cs program into Hello.exe so we can run it. FYI, you should still be in the Terminal/DOS window where we just listed the directory (this works regardless of what OS you are using). Enter:
gmcs Hello.cs
If everything worked right, you will not see any output. If you spot any error messages, it means that you probably made a typo when copying/typing the sample code into the text editor. Go back to step @EditHello and check that everything is typed properly. (We will not be discussing all the possible errors you an encounter at this stage, but you might find them helpful to edit your program.) If your text editor is not still open, then you need to re-open the file, which can be done easily by using File -> Open and browsing your folder structure to find folder hello, then Hello.cs.
Now for the great moment you have been awaiting: You can run Hello.exe. Enter:
mono Hello.exe
You should see the result:
Hello, World!
At this point, we have accomplished the major objective for Lab 0: to enter, compile, and run a C# program. In the next lab, we will work on some revisions to Hello.cs to personalize it a bit.
As this point, you should grab the instructor or teaching assistant so they can perform a quick inspection of your work and check it off. Per the syllabus, labs are not graded but do need to be completed to receive credit. If you are unable to make class on a lab day, please make sure that you complete the work and demonstrate it by the beginning of the next lab.
#. Gedit, http://gedit.org, is a very nice editor that comes with most Linux/Gnome distributions. Although it allegedly runs on Windows and OS X, we have not had a chance to test it and cannot recommend it at this time.
Unfortunately, these are not available in the Windows labs yet (unlike Emacs); however, students working in the Linux laboratory have access to these editors and may wish to learn them.
We’ll continue learning more about C#. The next lab will give you exposure to the C# interactive mode (in Mono, the csharp command), where we will learn to work with arithmetic and basic primitive types. The csharp command allows you to use C# as a sort of “toy calculator” language. It also allows you to test capabilities of the C# programming library. For example, we will learn some other things you can do with the Console interfaces, including how to prompt a user for input.